//! Rules by path every node judges a change by, the same way, before it applies it
//! (`judge`): who may write which part of the document. A change is judged by what it
//! touches (`document::inspect`), by who made it (its committer, the node a signature
//! proves, `document::signatures`; and the user its message names, `User:`), and by the
//! document as its writer saw it: at its dependencies (`document::at`), so a later
//! revocation doesn't refuse what was allowed when it was written, and every node,
//! whatever it holds since, judges alike.
//!
//! * A change without dependencies is an epoch's root: the genesis change, the first a
//!   document holds, or a remake's snapshot, whose hash is the epoch's ID. Nothing else
//!   is judged of it: it writes the protocol data it starts with.
//! * Any other is its committer's, a member at its dependencies, or registering itself,
//!   and not banned there (`access::bans`).
//! * Protocol data (`_continuum`, `document::meta`): a member's entry and its votes by
//!   that member only (removing an entry also by a user who may write there); epochs
//!   and the swarm ID in a root only; a remake's decision by the coordinator its
//!   proposal names, the rest of a record by any member; a user's tokens revoked by that
//!   user too (logging out); a member's forget record by that member too (cancelling it,
//!   alive); the rest by a user who may write there.
//! * User data: by a user who may write there.
//! * Under a strict policy (`access::policy`), the values their users sign
//!   (`access::envelope`) only as they signed them (`signed_values`).
//! * Where the swarm declares values sealed (`access::sealed`), only those sealed as
//!   declared (`sealed_values`).
//!
//! In a swarm without a user registry (`access::registry`), whatever a user would need,
//! any member may.

use std::collections::BTreeSet;

use crate::access::Right;
use crate::access::registry;
use crate::document::at::At;
use crate::document::inspect::{Action, Op, Path};
use crate::document::meta;
use crate::document::replica::Epoch;
use crate::document::{ChangeHash, Document, ReadDoc, store};

/// A change to judge, as its bytes say.
#[derive(Debug, Clone)]
pub(crate) struct Change<'a> {
    pub(crate) hash: ChangeHash,
    pub(crate) deps: &'a [ChangeHash],
    /// The heads to judge it at: its dependencies, or, for those not applied yet, the
    /// changes of the document they build on, where nothing between changed what rules
    /// read (`access::screen`).
    pub(crate) seen: &'a [ChangeHash],
    /// The node that made it (its node ID), as its signature proves.
    pub(crate) committer: Option<&'a str>,
    /// The user it names (`User:`), if any.
    pub(crate) user: Option<&'a str>,
    /// What it touches (`inspect::Inspector`).
    pub(crate) paths: &'a BTreeSet<Path>,
    /// Its operations, where each is and what it does there (`inspect::Inspector::ops`).
    pub(crate) ops: &'a [Op],
}

/// Why a change is refused.
#[derive(Debug, Clone, PartialEq, Eq)]
pub(crate) enum Refusal {
    /// Its dependencies aren't all in the document: it can't be judged yet.
    Unready,
    /// A rule refuses it: which, and what it touched.
    Rule(String),
}

impl std::fmt::Display for Refusal {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            Refusal::Unready => f.write_str("its dependencies aren't all here"),
            Refusal::Rule(why) => f.write_str(why),
        }
    }
}

/// Judges `change`, about to be applied to `doc` (of `epoch`).
pub(crate) fn judge(doc: &Document, epoch: Epoch, change: &Change<'_>) -> Result<(), Refusal> {
    if change.deps.is_empty() {
        // The first epoch's: the first change a document holds, as it comes to an empty
        // one, or as it is in one (judged again, `swarm::refusals`).
        let root = if epoch.generation == 0 {
            doc.get_heads().is_empty() || doc.get_change_by_hash(&change.hash).is_some()
        } else {
            change.hash.0 == epoch.id
        };
        return if root {
            Ok(())
        } else {
            Err(Refusal::Rule(
                "a change without dependencies that isn't the epoch's root".to_owned(),
            ))
        };
    }
    let at = At::new(doc, change.seen).ok_or(Refusal::Unready)?;
    let refuse = |why: String| Err(Refusal::Rule(why));
    let Some(node) = change.committer else {
        return refuse("it names no node".to_owned());
    };
    if super::bans::banned(&at, node) {
        return refuse(format!("{node} is banned"));
    }
    let own_entry = meta::path(&[meta::MEMBERS, node]);
    let member = store::read_path(&at, &own_entry).ok().flatten().is_some();
    let registering = change
        .paths
        .iter()
        .all(|path| path.starts_with(&own_entry) || *path == meta::path(&[meta::MEMBERS]));
    if !member && !registering {
        return refuse(format!("{node} isn't a member"));
    }
    let registry = registry::exists(&at);
    // Whether the user may write `path`: as the registry at its dependencies says, or,
    // without one, any member.
    let user_may = |path: &Path| match (registry, change.user) {
        (false, _) => true,
        (true, Some(user)) => registry::caps_of(&at, user).allows(Right::Write, path),
        (true, None) => false,
    };
    for path in change.paths {
        if !meta::is_protocol(path) {
            if !user_may(path) {
                return refuse(format!("{} may not write {}", who(change), shown(path)));
            }
            continue;
        }
        let part = path.get(1).map(String::as_str);
        let owner = path.get(2).map(String::as_str);
        let allowed = match (part, owner) {
            // A member's entry, its votes: its own. Removing an entry, also a user's.
            (Some(meta::MEMBERS), Some(owner)) => owner == node || user_may(path),
            (Some(meta::VOTES), Some(owner)) => owner == node,
            // What holds them, made by whichever member first writes in it.
            (Some(meta::MEMBERS | meta::VOTES | meta::REMAKES), None) => true,
            // Written by a root only.
            (Some(meta::EPOCHS | meta::SWARM), _) => false,
            // Logging out: a user revokes its own tokens (`POST /auth/logout`).
            (Some(meta::LOGOUTS), Some(owner)) => change.user == Some(owner) || user_may(path),
            // A node forgotten while alive cancels its own record (`swarm::peer::forget`).
            (Some(meta::FORGOTTEN), Some(owner)) => owner == node || user_may(path),
            (Some(meta::REMAKES), Some(id)) => match path.get(3).map(String::as_str) {
                // Its coordinator's; or a record carried into a new epoch whole, by the
                // node that coordinated it (`remake::switch`): its proposal written with it.
                Some("decision") => match coordinator(&at, id) {
                    Some(coordinator) => coordinator == node,
                    None => {
                        change
                            .paths
                            .iter()
                            .any(|other| other == &meta::path(&[meta::REMAKES, id, "proposal"]))
                            || change
                                .paths
                                .iter()
                                .any(|other| other == &meta::path(&[meta::REMAKES, id]))
                    }
                },
                _ => true,
            },
            _ => user_may(path),
        };
        if !allowed {
            return refuse(format!("{} may not write {}", who(change), shown(path)));
        }
    }
    if super::policy::of(&at).strict() {
        signed_values(&at, change.ops).or_else(refuse)?;
    }
    let declared = super::sealed::declared(&at);
    if !declared.is_empty() {
        sealed_values(&at, &declared, change.ops).or_else(refuse)?;
    }
    Ok(())
}

/// Where values are declared sealed (`declared`), `ops` write only sealed values as
/// declared, judged at `at`, as their writer saw it (`sealed::check`): at such a place, a
/// string put there that is one (or deleting what is there); nothing within one; nothing
/// in an object nowhere to be found, which might be one.
fn sealed_values(
    at: &At<'_>,
    declared: &[super::sealed::Declared],
    ops: &[Op],
) -> Result<(), String> {
    for op in ops {
        let path = &op.path;
        if op.action == Action::Nowhere {
            return Err("it writes in an object nowhere to be found".to_owned());
        }
        if let Some(place) = super::sealed::place(declared, path) {
            match &op.action {
                Action::PutString(text) => {
                    super::sealed::check(at, place, &serde_json::Value::String(text.clone()))
                        .map_err(|why| format!("{}: {why}", shown(path)))?;
                }
                Action::Delete => {}
                _ => return Err(format!("{} holds a sealed value", shown(path))),
            }
        } else if super::sealed::within(declared, path) {
            return Err(format!("{} is within a sealed value", shown(path)));
        }
    }
    Ok(())
}

/// Under a strict policy, `ops` change the values their users sign (`access::envelope`)
/// only as they signed them, judged at `at`, as their writer saw it: at such a place, a
/// string put there that is an envelope by a user who may write there, replacing the
/// one there (`envelope::check`), and nothing else (but deleting what is there first,
/// as a write replacing it does); nothing within one; above one,
/// nothing replacing or deleting what holds one (a map made where there is none yet,
/// what is inside a list or text, which holds none).
fn signed_values(at: &At<'_>, ops: &[Op]) -> Result<(), String> {
    let signed = super::envelope::signed_paths(at);
    for op in ops {
        let path = &op.path;
        if op.action == Action::Nowhere {
            return Err("it writes in an object nowhere to be found".to_owned());
        }
        if super::envelope::is_signed(&signed, path) {
            let replaced = || {
                ops.iter().any(|other| {
                    other.path == *path && matches!(other.action, Action::PutString(_))
                })
            };
            let envelope = match &op.action {
                Action::PutString(envelope) => envelope,
                // Cleared for the string put there, which is checked.
                Action::Delete if replaced() => continue,
                _ => return Err(format!("{} holds a value its user signs", shown(path))),
            };
            let previous = match store::read_path(at, path) {
                Ok(Some(serde_json::Value::String(text)))
                    if super::envelope::read(&text).is_ok() =>
                {
                    Some(text)
                }
                _ => None,
            };
            super::envelope::check(at, envelope, path, previous.as_deref())
                .map_err(|why| format!("{}: {why}", shown(path)))?;
        } else if super::envelope::signed_path(&signed, path).is_some() {
            return Err(format!("{} is within a value its user signs", shown(path)));
        } else if op.action != Action::Within
            && super::envelope::above_signed(&signed, path)
            && holds_signed(at, path, &signed)
        {
            return Err(format!("{} holds values their users sign", shown(path)));
        }
    }
    Ok(())
}

/// Whether what is at `path` in `at` holds a value at a place for one its user signs,
/// of `signed` (`envelope::signed_paths`), signed or from before the policy; one that
/// doesn't read, as if it did.
fn holds_signed(at: &At<'_>, path: &[String], signed: &[Vec<String>]) -> bool {
    fn within(value: &serde_json::Value, place: &mut Vec<String>, signed: &[Vec<String>]) -> bool {
        if super::envelope::is_signed(signed, place) {
            return true;
        }
        match value {
            serde_json::Value::Object(entries) if super::envelope::above_signed(signed, place) => {
                entries.iter().any(|(key, value)| {
                    place.push(key.clone());
                    let holds = within(value, place, signed);
                    place.pop();
                    holds
                })
            }
            _ => false,
        }
    }
    match store::read_path(at, path) {
        Ok(Some(value)) => within(&value, &mut path.to_vec(), signed),
        Ok(None) => false,
        Err(_) => true,
    }
}

/// Who wrote it, for a refusal.
fn who(change: &Change<'_>) -> String {
    match (change.committer, change.user) {
        (Some(node), Some(user)) => format!("{user} at {node}"),
        (Some(node), None) => node.to_owned(),
        (None, _) => "nobody".to_owned(),
    }
}

fn shown(path: &Path) -> String {
    format!("/{}", path.join("/"))
}

/// The coordinator remake `id`'s proposal names, at `at`.
fn coordinator(at: &At<'_>, id: &str) -> Option<String> {
    let proposal = store::read_path(at, &meta::path(&[meta::REMAKES, id, "proposal"]))
        .ok()
        .flatten()?;
    proposal
        .get("coordinator")
        .and_then(serde_json::Value::as_str)
        .map(str::to_owned)
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::clock::UnixMillis;
    use crate::document::replica::{Writer, transact};
    use serde_json::json;

    fn path(text: &str) -> Path {
        text.split('/').map(str::to_owned).collect()
    }

    fn paths(texts: &[&str]) -> BTreeSet<Path> {
        texts.iter().map(|text| path(text)).collect()
    }

    fn write(doc: &mut Document, at: &str, value: serde_json::Value) {
        let writer = Writer {
            node: "genesis",
            user: None,
        };
        let at = path(at);
        transact(doc, UnixMillis(1), &writer, |doc| {
            store::write_path(doc, &at, &value)
        })
        .unwrap();
    }

    /// A swarm with members `a` and `b`, a remake proposed by `a`, and, if `users`,
    /// user `alice` who may write `notes` and `bob` who may not write at all.
    fn swarm(users: bool) -> Document {
        let mut doc = Document::new();
        write(&mut doc, "_continuum/swarm", json!("s"));
        write(&mut doc, "_continuum/members/a", json!({"since": 1}));
        write(&mut doc, "_continuum/members/b", json!({"since": 1}));
        write(
            &mut doc,
            "_continuum/remakes/r1/proposal",
            json!({"coordinator": "a"}),
        );
        if users {
            let alice = registry::entry("a", 1, &[(path("notes"), &[Right::Write][..])]);
            write(&mut doc, "_continuum/users/alice", alice);
            write(
                &mut doc,
                "_continuum/users/bob",
                registry::entry("a", 1, &[]),
            );
        }
        doc
    }

    fn judged(
        doc: &Document,
        committer: &str,
        user: Option<&str>,
        touched: &[&str],
    ) -> Result<(), Refusal> {
        let deps = doc.get_heads();
        let touched = paths(touched);
        judge(
            doc,
            Epoch::GENESIS,
            &Change {
                hash: ChangeHash([9; 32]),
                deps: &deps,
                seen: &deps,
                committer: Some(committer),
                user,
                paths: &touched,
                ops: &[],
            },
        )
    }

    fn refused(result: Result<(), Refusal>) -> bool {
        matches!(result, Err(Refusal::Rule(_)))
    }

    /// A member's entry and votes are its own; epochs and the swarm ID a root's.
    #[test]
    fn protocol_data() {
        let doc = swarm(true);
        assert!(judged(&doc, "a", None, &["_continuum/members/a/alive"]).is_ok());
        assert!(refused(judged(
            &doc,
            "a",
            None,
            &["_continuum/members/b/alive"]
        )));
        assert!(judged(&doc, "b", None, &["_continuum/votes/b"]).is_ok());
        assert!(refused(judged(&doc, "a", None, &["_continuum/votes/b"])));
        assert!(refused(judged(&doc, "a", None, &["_continuum/swarm"])));
        assert!(refused(judged(&doc, "a", None, &["_continuum/epochs/1"])));
        // A remake's decision: its coordinator's; the rest of the record, any member's.
        assert!(judged(&doc, "a", None, &["_continuum/remakes/r1/decision"]).is_ok());
        assert!(refused(judged(
            &doc,
            "b",
            None,
            &["_continuum/remakes/r1/decision"]
        )));
        assert!(judged(&doc, "b", None, &["_continuum/remakes/r1/abortRequested"]).is_ok());
        // A record carried into a new epoch whole: its proposal with its decision.
        assert!(
            judged(
                &doc,
                "b",
                None,
                &[
                    "_continuum/remakes/r2",
                    "_continuum/remakes/r2/proposal",
                    "_continuum/remakes/r2/decision"
                ]
            )
            .is_ok()
        );
        assert!(refused(judged(
            &doc,
            "b",
            None,
            &["_continuum/remakes/r2/decision"]
        )));
        // The rest: a user's who may write there.
        assert!(refused(judged(&doc, "a", None, &["_continuum/neighbours"])));
        assert!(refused(judged(
            &doc,
            "a",
            Some("alice"),
            &["_continuum/neighbours"]
        )));
        // Logging out: its own tokens only.
        let tokens = "_continuum/logouts/bob";
        assert!(judged(&doc, "a", Some("bob"), &[tokens]).is_ok());
        assert!(refused(judged(&doc, "a", Some("alice"), &[tokens])));
        // A forget record: cancelled by the node it names, not by another.
        let forgotten = "_continuum/forgotten/a";
        assert!(judged(&doc, "a", None, &[forgotten]).is_ok());
        assert!(refused(judged(&doc, "b", None, &[forgotten])));
    }

    /// A banned node's changes: refused, as the ban stood when they were made.
    #[test]
    fn banned_nodes() {
        let mut doc = swarm(true);
        let before = doc.get_heads();
        write(&mut doc, "_continuum/banned/b", json!({"by": "alice"}));
        assert!(refused(judged(
            &doc,
            "b",
            None,
            &["_continuum/members/b/alive"]
        )));
        let touched = paths(&["_continuum/members/b/alive"]);
        let earlier = judge(
            &doc,
            Epoch::GENESIS,
            &Change {
                hash: ChangeHash([9; 32]),
                deps: &before,
                seen: &before,
                committer: Some("b"),
                user: None,
                paths: &touched,
                ops: &[],
            },
        );
        assert!(earlier.is_ok());
    }

    /// A node that isn't a member may only register itself.
    #[test]
    fn strangers_register_themselves_only() {
        let doc = swarm(false);
        assert!(
            judged(
                &doc,
                "c",
                None,
                &[
                    "_continuum/members",
                    "_continuum/members/c",
                    "_continuum/members/c/alive"
                ]
            )
            .is_ok()
        );
        assert!(refused(judged(&doc, "c", None, &["notes/x"])));
        assert!(refused(judged(&doc, "c", None, &["_continuum/members/a"])));
    }

    /// User data: as the registry at the change's dependencies says; without one, any
    /// member's.
    #[test]
    fn user_data() {
        let doc = swarm(true);
        assert!(judged(&doc, "a", Some("alice"), &["notes/x"]).is_ok());
        assert!(refused(judged(&doc, "a", Some("alice"), &["config"])));
        assert!(refused(judged(&doc, "a", Some("bob"), &["notes/x"])));
        assert!(refused(judged(&doc, "a", None, &["notes/x"])));
        assert!(refused(judged(&doc, "a", Some("nobody"), &["notes/x"])));
        let legacy = swarm(false);
        assert!(judged(&legacy, "a", None, &["notes/x"]).is_ok());
        assert!(judged(&legacy, "a", None, &["_continuum/neighbours"]).is_ok());
    }

    /// Judged by the registry its writer saw: a revocation since refuses nothing it
    /// allowed then.
    #[test]
    fn judged_as_its_writer_saw_it() {
        let mut doc = swarm(true);
        let then = doc.get_heads();
        write(
            &mut doc,
            "_continuum/users/alice",
            registry::entry("a", 2, &[]),
        );
        let touched = paths(&["notes/x"]);
        let change = |deps: &[ChangeHash]| {
            judge(
                &doc,
                Epoch::GENESIS,
                &Change {
                    hash: ChangeHash([9; 32]),
                    deps,
                    seen: deps,
                    committer: Some("a"),
                    user: Some("alice"),
                    paths: &touched,
                    ops: &[],
                },
            )
        };
        assert!(change(&then).is_ok());
        assert!(refused(change(&doc.get_heads())));
        // Unknown dependencies: not judged yet.
        assert_eq!(change(&[ChangeHash([7; 32])]), Err(Refusal::Unready));
    }

    /// Under a strict policy, a value its user signs only as signed: an envelope that
    /// checks, replacing the one there; nothing else there, nothing within one, nothing
    /// above replacing what holds one.
    #[test]
    fn signed_values_as_signed() {
        use crate::access::{envelope, sshsig};
        let key = ed25519_dalek::SigningKey::from_bytes(&[3; 32]);
        let mut doc = swarm(false);
        let mut alice = registry::entry(
            "a",
            1,
            &[
                (Vec::new(), &[Right::Write][..]),
                (path("_continuum"), &[Right::Write][..]),
            ],
        );
        alice["keys"] = json!({ "k": sshsig::PublicKey(key.verifying_key().to_bytes()).line() });
        write(&mut doc, "_continuum/users/alice", alice);
        write(
            &mut doc,
            "_continuum/access/userSigned",
            json!([["config"], ["a", "b"]]),
        );
        write(
            &mut doc,
            "_continuum/access/policy",
            json!({"version": 1, "values": "signed"}),
        );
        let sealed = |at: &str, prev: &str| {
            let payload = envelope::Payload {
                path: path(at),
                value: json!({"mode": "fast"}),
                user: "alice".to_owned(),
                at: 1,
                prev: prev.to_owned(),
            };
            let bytes = serde_json::to_vec(&payload).unwrap();
            envelope::seal(&bytes, &sshsig::sign(&key, envelope::NAMESPACE, &bytes)).unwrap()
        };
        let judged = |doc: &Document, ops: Vec<Op>| {
            let deps = doc.get_heads();
            let touched: BTreeSet<Path> = ops.iter().map(|op| op.path.clone()).collect();
            judge(
                doc,
                Epoch::GENESIS,
                &Change {
                    hash: ChangeHash([9; 32]),
                    deps: &deps,
                    seen: &deps,
                    committer: Some("a"),
                    user: Some("alice"),
                    paths: &touched,
                    ops: &ops,
                },
            )
        };
        let op = |at: &str, action: Action| Op {
            path: path(at),
            action,
        };
        let first = sealed("config", "");
        assert!(judged(&doc, vec![op("config", Action::PutString(first.clone()))]).is_ok());
        assert!(refused(judged(
            &doc,
            vec![op("config", Action::PutString("plain".to_owned()))]
        )));
        assert!(refused(judged(
            &doc,
            vec![op("config", Action::PutString(sealed("other", "")))]
        )));
        assert!(refused(judged(&doc, vec![op("config", Action::Delete)])));
        assert!(refused(judged(
            &doc,
            vec![
                op("config", Action::Delete),
                op("config", Action::PutString("plain".to_owned()))
            ]
        )));
        assert!(refused(judged(&doc, vec![op("config/x", Action::Other)])));
        // Replacing: only the one there.
        write(&mut doc, "config", json!(first));
        let second = sealed("config", &envelope::digest(Some(&first)));
        assert!(judged(&doc, vec![op("config", Action::PutString(second.clone()))]).is_ok());
        // As a write replacing it makes it: what is there deleted, then the string put.
        assert!(
            judged(
                &doc,
                vec![
                    op("config", Action::Delete),
                    op("config", Action::PutString(second))
                ]
            )
            .is_ok()
        );
        assert!(refused(judged(
            &doc,
            vec![op("config", Action::PutString(sealed("config", "")))]
        )));
        // Above: a map made where there is none, not what holds a signed value.
        assert!(judged(&doc, vec![op("a", Action::MakeMap)]).is_ok());
        assert!(refused(judged(
            &doc,
            vec![op("_continuum/users", Action::Delete)]
        )));
        assert!(refused(judged(
            &doc,
            vec![op("_continuum/users/alice/caps", Action::Other)]
        )));
        // Elsewhere: as without the policy.
        assert!(judged(&doc, vec![op("notes/x", Action::PutString("x".to_owned()))]).is_ok());
        assert!(refused(judged(&doc, vec![op("", Action::Nowhere)])));
    }

    /// Where values are declared sealed: only sealed ones, as declared, with or without
    /// a strict policy.
    #[test]
    fn sealed_values_as_declared() {
        use crate::access::sealed::testing::sealed_for;
        use crate::access::sshsig::PublicKey;
        let key = PublicKey([8; 32]);
        let mut doc = swarm(true);
        let mut alice = registry::entry("a", 2, &[(Vec::new(), &[Right::Write][..])]);
        alice["keys"] = json!({ "k": key.line() });
        write(&mut doc, "_continuum/users/alice", alice);
        write(
            &mut doc,
            "_continuum/access/sealed",
            json!([{"path": ["secrets", "*"], "readers": ["alice"]}]),
        );
        let judged = |ops: Vec<Op>| {
            let deps = doc.get_heads();
            let touched: BTreeSet<Path> = ops.iter().map(|op| op.path.clone()).collect();
            judge(
                &doc,
                Epoch::GENESIS,
                &Change {
                    hash: ChangeHash([9; 32]),
                    deps: &deps,
                    seen: &deps,
                    committer: Some("a"),
                    user: Some("alice"),
                    paths: &touched,
                    ops: &ops,
                },
            )
        };
        let op = |at: &str, action: Action| Op {
            path: path(at),
            action,
        };
        let sealed = sealed_for(&[key]);
        assert!(judged(vec![op("secrets/db", Action::PutString(sealed))]).is_ok());
        assert!(judged(vec![op("secrets/db", Action::Delete)]).is_ok());
        assert!(refused(judged(vec![op(
            "secrets/db",
            Action::PutString("hunter2".to_owned())
        )])));
        let stray = sealed_for(&[key, PublicKey([9; 32])]);
        assert!(refused(judged(vec![op(
            "secrets/db",
            Action::PutString(stray)
        )])));
        assert!(refused(judged(vec![op("secrets/db", Action::MakeMap)])));
        assert!(refused(judged(vec![op(
            "secrets/db/password",
            Action::Other
        )])));
        assert!(judged(vec![op("notes/x", Action::PutString("plain".to_owned()))]).is_ok());
    }

    /// Roots: the first change of a swarm's first epoch, a later epoch's snapshot.
    #[test]
    fn roots() {
        let root = |doc: &Document, epoch: Epoch, hash: [u8; 32]| {
            let touched = paths(&["_continuum/swarm"]);
            judge(
                doc,
                epoch,
                &Change {
                    hash: ChangeHash(hash),
                    deps: &[],
                    seen: &[],
                    committer: None,
                    user: None,
                    paths: &touched,
                    ops: &[],
                },
            )
        };
        assert!(root(&Document::new(), Epoch::GENESIS, [1; 32]).is_ok());
        assert!(refused(root(&swarm(false), Epoch::GENESIS, [1; 32])));
        // The first epoch's, judged again in a document that holds it: its root.
        let held = swarm(false);
        let first = held.get_changes(&[])[0].hash();
        assert!(root(&held, Epoch::GENESIS, first.0).is_ok());
        let epoch = Epoch {
            generation: 3,
            id: [5; 32],
        };
        assert!(root(&swarm(false), epoch, [5; 32]).is_ok());
        assert!(refused(root(&swarm(false), epoch, [6; 32])));
    }
}